1. Field of the Invention
The present invention relates to an apparatus for producing a silicon ingot, and more particularly, to an apparatus for producing a polycrystalline silicon ingot used for a solar cell.
2. Background Art
Recently, according to an increase of the demand of solar cells of several tens percents or so yearly, the demand of polycrystalline silicon ingots for the solar cells is also increased greatly every year. In general, the polycrystalline silicon ingot for the solar cell is produced through the steps of charging a raw silicon material into a quartz or graphite crucible and melting it, followed by directional solidification.
FIG. 1 is a sectional view of an apparatus for producing a polycrystalline semiconductor ingot according to the prior art.
Referring to FIG. 1, the apparatus for producing the polycrystalline semiconductor ingot disclosed in U.S. Pat. No. 6,136,091 will be described. The apparatus for producing the polycrystalline semiconductor ingot includes: a main body 140 having a chamber consisting of a hot zone therein; a quartz or graphite crucible 170 for containing a raw silicon material therein; supporting means (not shown) for supporting the quartz or graphite crucible 170; a sectional type rectangular heater 110 aligned around the crucible 170 to supply radiant heat energy for melting the raw silicon material; another crucible 170′ for intercepting heat emitted around the quartz or graphite crucible 170; an insulating member 190 aligned around the sectional type rectangular heater 110; and a cooling jacket 160 having a cooling water inlet line 150 and a cooling water outlet line 180 for controlling temperature of the apparatus. So, a crucible protective layer is coated on the inner surface of the quartz or the graphite crucible, the raw silicon material is charged into the crucible, and then, the crucible and the completed sectional type rectangular heater are assembled to a casting device.
After the crucible and the sectional type rectangular heater are assembled to the inside of the casting device, vacuum is applied to the device to remove the air inside the device, and then, argon gas is supplied into the device of a vacuum state to change the internal pressure of the device into atmospheric pressure. The above process is repeatedly performed three times. After that, cooling water is supplied to cool the wall surface of the device, and continuously, power source is supplied to the sectional type rectangular heater to heat the inside temperature of the crucible up to more than 1,450° C. The above state is kept for more than two hours. When silicon charged into the crucible is completely melted, the power source supplied to the sectional type rectangular heater is controlled such that the crucible is cooled to the upper portion thereof from the lower portion thereof.
However, since the cooling of the crucible proceeding from the lower portion thereof to the upper portion thereof is not uniform only by the control of the power source supplied to the heater, it is difficult to achieve a uniform crystal growth, and ununiformity of a physical property of the ingot may be caused.
Japanese Patent Nos. 11,092,284 and 11,116,386 disclose an improved production of silicon ingot having a polycrystal structure coagulated in one direction. In Japanese Patent Nos. 11,092,284 and 11,116,386, for more improved temperature control, provided are a vertically movable crucible 170 and a conveying shaft located at the central portion of a pedestal. However, such prior art arrangement exhibit a problem in that heat applied to the crucible 170 escapes to the outside through the conveying shaft to cause a loss of heat.
It follows that the efficiency of the prior art arrangements is poor.
DE-A-19855061 discloses a melting furnace that includes a heater fired beneath a crucible and a horizontally moveable cooking plate.